Corn planting proceeded at an all-time record this spring. Iowa experienced one of the best planting seasons ever. According to the most recent USDA-NASS report (May 2, 2010), 84% of Iowa’s corn was planted with cropping districts ranging from 69% complete in south-central Iowa to 92% complete in north-central Iowa. Overall, corn has been planted within the recommended window, which should serve to maximize yield potential relative to planting date.

Soil and weather conditions at planting and emergence were excellent for most of the state. Alison Robertson recently emphasized the need to assess seedling health when doing stand counts in a May 4, 2010 ICM article in response to some of the problems occurring in southeast Iowa this spring. Seedling emergence problems there are correlated with swings in April soil temperature.

Cooler soil temperatures slow the germination process and predispose seedlings to fungal infection. We have also observed, or heard reports of, seedling growth problems in some parts of Iowa already this year, including:

  • Imbibitional chilling damage, which is the chilling effect seeds may experience when they imbibe, or absorb, water when soil temperatures are less than 55° F for an extended time. Seedlings may “corkscrew” or not emerge when exposed to these cool soil temperatures. This may happen also when there are rapid swings in air temperatures of nearly 30° F.

  • Soil crusting due to wet soils at planting or heavy rains after planting reducing plant stands. Significant stand reductions lower yield potential.

  • “Leafing out” underground. This occurs most often in crusted soils and also appears associated with imbibitional chilling, mentioned above.

  • Variable plant emergence and reduced plant population. Variable emergence and growth will reduce yield.

Cool temperatures soon?
The forecast for the next several days is for air temperatures dropping into the high 30s at night; soil temperatures will also lower respectively. Growers and agronomists should pay particular attention to cornfields planted recently, as they are the most likely to exhibit seedling rot or poorer emergence associated with some of the issues mentioned here. Frost is likely to occur in low-lying areas causing leaf necrosis and delayed growth of sprouted seeds.

Any of the situations mentioned above may result in a need to replant. Assess stands well before making this decision.

Irrespective of all of these issues, 2010 has provided one of the best planting seasons to date. Most of Iowa’s corn was planted within a timeframe that should serve to maximize yield potential.